Fluidization of Large Char and Coal Particles

Abstract

In order to support the fluidized bed combustion of large size solid fuel, a study of the mixing and fluidization of char (15mm under) and coal particles (25mm under) was conducted using a laboratory-scale fluidized bed. The axial concentration profiles of the char and coal particles were measured under various conditions, and the degree of mixing was evaluated by the mixing index, M, which was defined in the present paper.
The mixing index M of the char particles approaches unity, i. e. perfect mixing, with the increase in gas velocity or the decrease in bed height. When the excess gas velocity, u₀-u_mf has a constant value, the index M of the char particles is not affected by the difference in the mean diameter of the fluidized particles.
The degree of mixing of the coal particles is also promoted with the increase in gas velocity. The use of fluidized particles which have a higher bulk density and a higher value of minimum fluidizing velocity can restrict the deposition of the coal particles on the distributor plate.
Several design factors for the fluidized bed combustor of large size solid fuel are also discussed on the basis of the present results.